Foam conductor for oil tanks



Oct. 29, 1929. AMOELLER- 1,733,551

FOAM CONDUCTOR FOR OIL TANKS Filed Nov. 1927 v 1 5 I E I O a V w O I O J00 O O '\Q To 1 BENJAMIN A' MUELLER BY INVENTOR flaw! AT RNEY PatentedOct. 29, 1929 UNITED STATES PATENT OFFICE FOAM CONDUCTOR FOR OIL TANKSApplication filed November 7, 1927. Serial No. 231,697.

In the extinguishing of fires occurring in tanks containing oil, it iscustomary to produce a fire foam and to project it through the roof ofthe tank, usually at a point close to its side, in order to produce alayer of the foam over the surface of the burning oil.

It is well known that foam falling for a considerable distance, as forinstance where the tank is only partly filled, is materially depreciatedin value by breaking down as it forcibly strikes the surface of the oil,while if it is carried below surface it is likely to produce a seriousand highly detrimental frothing.

To overcome this difficulty several devices have been roposed by meansof which the foam may e lowered gently to a point just above the burningsurface. The object of my invention is to provide a cheap and simplemeans for accomplishing this object, and the advantages of my inventionwill be apparent on inspection of the drawing appended hereto and thefollowing description thereof. This drawing represents partly inelevation and partly in cross section a portion of a tank containing oiland my improved means for introducing foam onto the surface of said oil.Referring to the drawing, 1 is the bottom of a tank, 2 is a section ofits side wall, 3 is a section of a portion of its roof and 4 indicatesthe rim of the tank proper. The pipes 5 and 6 discharge two dissimilarfoam producing solutions into a mixing head of usual or preferred designby which the solutions are thoroughly comingled and converted into foam.I would have it understood that this mixing head is no part of myinvention and that the'foam with which the fire is to be extinguishedmay be generated in any manner, in any kind of apparatus, and may beconducted over the rim of the tank by any convenient means. N

8 is a pipe of a size proportionate to the size of the tank. For a tankof standard construction having a capacity of-55,000 barrels I prefer touse standard pipe of 15 inches diameter, but I do not restrict myself toany particular diameter of pipe nor to any particular material.

The lower end of this pipe should terminate on or closely above thebottom 1 of the tank as indicated at 9. Through this pipe, andsubstantially throughout its length, perforations as indicated at 10should be formed at substantially regular intervals, the spacing anddiameter of these perforations being such that the area of theperforations in three lineal feet of the perforated pipe will equal thearea of the foam inlet over the rim of the tank. For instance, in a 15inch pipe I preferably use two inch perforations so spaced that thetotal number of perforations in three lineal feet length of the 15'inchpipe will have a combined area equal to two and one fourth square feet,which is the area of the inlet of the standard mixing head abovereferred to. Smaller or larger pipes should preferably havecorrespondingly graduated perforations of size varying directly with thediameter.

This particular ratio of perforation area to inlet area figures to 108two inch perforations per lineal foot of pipe, and the ratio ofperforation area to pipe area is 0.6 to 1.0. This ratio has beendemonstrated to give good results in pipes of this size, which areprobably as large as would be used in the largest tanks now being built.In pipes of smaller size the ratio of perforation to pipe would have tobe greater because of the greater relative resistance of smallerperforations. The object of the perforations is to retain within thedown pipe just sufficient head of foam to cause it to emerge mainlythrough the perforations close to the oil, without jet-ting through theholes or leaving the outer surface of the pipe other than by flowingdown such outer surface. lVith this object in mind it is easy todetermine by simple experiments the correct perforation area (which canbe carried over quite a wide range) suitable for any given down pipesize.

While I have shown round perforations,

as being the most convenient to form in practice, my invention is by nomeans limited to such shape, slots or holes of any preferred shapeanswering the same purpose, which is simply to restrict the outflow areasufiiciently to produce a gentle welling out of the foam from the lowerperforations. Battery screen having slot areas suitable to the sizepipes to be made may be advantageously rolled up and Welded into downpipes of smaller sizes. c it is not necessary to close or even tosubstantially close the lower end of pipe 8, it is desirable to do soand I prefer to effect this closure at oil level, by means of a floatingpiston 11 substantially fitting the inside of pipe 8 but not fitting soclosely as to incur any danger of the piston sticking. This piston isclosed on the bottom as indicated at 12 and also has a horizontal webindicated at 13, which is preferably placed below the upper end of thepiston wall, leaving the open cup indicated at 14. The object of theiston is to prevent foam from escaping om pipe 8 beneath the surface ofthe oil, and its buoyancy should be such as to cause the upper end ofthe piston to stand substantially at the level of the oil in the tank,or at a point rather lower than thatindicated in the drawing in whichthe oil level is indicated at 15. For a pipe 15 inches in diameter thebuoyancy of the piston should be such that a weight of 100 pounds isrequired to force it down to the preferred level above described.Pistons of difi'erent diameters would obviously require difierentdegrees of buoyancy.

The open cup 14 is not an essential part of my invention, though its useis highly desirable. It has been found that where'the upper end of thepiston is convex or even fiat,

there is a decided tendency for foam to leak past the piston and makeits way out of the perforations below the piston, or even from thebottom of the pipe. This tendency is ofi' set, for reasons which are notfully understood, by providing a substantially concave upper end such asthe cup described.

The operation of my invention will already have been made evident by theabove description. Foam pumped into the upper end of the perforated pipe8 flows down inside the pipe and emerges above the piston 14 through theholes 10. Where these holes have such an area that three lineal feet ofthe pipe provides openings equivalent to the area of the foam inlet, thefoam will actually emerge from the pipe for a distance ranging from fourto five feet above the top of the piston.

The foam thus gently emitted from the relatively small holes is observedto flow down the outside of the pipe in a semi-fluid mass, usually ofconsiderable thickness as meas: ured from the outer surface of the pipe.This mass flows down onto the oil surface 15 with the least possibledisturbance of that surface, and spreads out rapidly and evenly into asmooth and unbroken layer. Such small uantities of foam'as may emergefrom perorations above the level stated will not leave the outer surfaceof the pipe, but will flow down gently to join the mass of foam flowingout of the lower perforations.

My invention thus provides for the floating on the surface of a layer ofbnrnin oil of a consistent layer of fire foam wit out any dangerwhatever of the breaking down of the foam or of the projection of massesof foam beneath the surface of the. burning oil.

I claim as my invention:

1.- In a device for placing fire foam on a surface of a layer of oilconfined in a tank, an unobstructed pipe extending from the upperportion of the tank to substantially" its bottom, said pipe beingperforated substantially throughout its entire length with holes havinga suficient combined area to permit the outflow of foam discharged intothe upper end of said pipe, each of said holes being of materially lessarea than the pipe and being unobstructed both within and without saidpipe, a piston float g within said pipe, said piston being soconstructed as to float substantially at the level of the oil containedin said tank. I

2. A device substantially as-and for the purpose set forth in claim 1,wherein said piston has its upper end formed into a cup openingupwardly.

In witness that I claim the foregoing 'I have hereunto subscribed myname this 21st day of October, 1927.

BENJ A. MUELLER.

